This invention relates to an auto-ignition, direct-injection internal combustion engine.
In direct-injection internal combustion engines with auto-ignition, in order to optimize combustion, use is made of different piston depression shapes which define the corresponding combustion chamber configuration and influence the combustion in the combustion chamber. This is intended to improve the mixture formation in the combustion chamber and therefore the formation of emissions in the exhaust gas. It is also possible to optimize the operation of an exhaust gas after treatment system arranged downstream.
A piston depression having a compression hump is known from German document DE 100 28 449 A1. The basic shape of the compression hump approximately forms a spherical cap. In the region of a maximum depression depth, the depression has an annular diameter which is less than half of the piston diameter. This is intended to make the piston suitable, as a result of its mechanical and thermal durability, for higher combustion pressures, so that it is possible to obtain higher levels of efficiency and power.
One object of the invention is the object of providing an auto-ignition internal combustion engine in which the mixture formation and the combustion in the combustion chamber are improved. This is achieved by means of a device having the features claimed.
According to a first embodiment, below a horizontal plane which is aligned with an uppermost part of the depression edge, the piston depression has a depression volume and is formed in such a way that a quotient of maximum depression depth divided by depression volume is in a range between 0.05 and 0.35, and in particular between 0.1 and 0.25. This provides an optimized design of the combustion chamber with regard to the fuel mass distribution in the available piston depression volume, so that sufficient oxygen proportions are available for combustion before and/or during the auto-ignition process. Soot particle formation is thereby minimized or largely impeded. The dimensions and ratios provided according to the invention form an adapted overall surface of the depression interior, by means of which the formation of fuel-rich zones within the depression volume according to the invention is almost completely avoided or considerably reduced. The effects surprisingly obtained with the ratios according to the invention are predominantly obtained as a result of the favorable trade-off between the intensive distribution of the fuel particles and in particular of the obtained mixture depth of the fuel droplets in relation to the depression volume.
According to a second embodiment, the piston depression is enclosed by an annular depression edge with a maximum depression diameter, and the piston has a piston diameter, and a ratio of piston diameter to maximum depression diameter is in a range between 1.05 and 1.4 or between 1.05 and 1.3. The ratio is preferably in a range from 1.1 to 1.2. This causes a remarkably fast propagation of the fuel mass within the piston depression, and therefore a rapid mixture of the fuel with the air. A fuel particle distribution is obtained which is matched to the piston diameter, which fuel particle distribution, according to the invention, permits an above-average propagation of fuel and therefore considerable mixture with the combustion air within the depression. The formation of fuel-rich zones at critical points in the combustion chamber is thereby reduced to a minimum.
According to a third embodiment, the injection bores and the compression projection are formed such that a generated ratio of fuel cone angle to depression angle is in a range between 0.95 and 1.36, and in particular between 1.15 and 1.3. The injected fuel mass is therefore distributed uniformly within the piston depression, and a mixture of fuel with combustion air is intensified. Accordingly, the provided ratio or the adaptation of the fuel cone angle to the depression angle provides a combustion chamber configuration which generates an adapted interaction within the piston depression between the depression contour profile and a fuel mass which emerges from the injection nozzle. If the projection is of conical design, then a cone angle is incorporated as a depression angle, wherein the projection can have other shapes, for example a spherical design. A tangent adjoining the projection with a corresponding angle of inclination can then be incorporated to determine the depression angle.
The effects obtained are to be predominantly attributed to a favorable trade-off between the angle at which the fuel particles impinge on the depression, and the obtained penetration depth of the fuel droplets in relation to the depression angle. This makes it possible to obtain sufficient mixture of the fuel droplets with the combustion air. The distribution of the injected fuel within the piston depression and the subsequent mixture with the combustion air therefore takes place before the initiation of undesired soot particle formation, in particular during full-load operation.
According to a further embodiment of the invention, the piston depression has a diameter in the depression base at a maximum depression depth, and a ratio of the diameter at the maximum depression depth to the piston diameter is in a range between 0.22 and 0.45, and in particular between 0.3 and 0.39. According to the invention, flow conditions which are adapted to the piston diameter are formed in the proposed range, which flow conditions permit a fast and sufficient mixture of the fuel jets with combustion air in the lower depression region. Turbulent flow movements are therefore obtained which largely prevent the formation of fuel-rich zones in the lower depression range.
In a further embodiment of the invention, a piston depression contour has a depression base radius between the depression base and the depression edge, and a ratio of depression base radius to maximum depression diameter is in a range between 0.1 and 0.35, and in particular between 0.16 and 0.22. This ensures uniform and controlled guidance of the fuel particles along the piston depression base. This then leads, in a targeted fashion, to more intense mixture of the fuel with the combustion air. In addition, a sufficient contact surface is provided, which is adapted to the piston depression size, between the combustion air and the fuel jets sliding on the depression base.
According to a further embodiment of the invention, the piston depression contour has a projection radius between the compression projection and the depression base, and a ratio of projection radius to maximum depression diameter is in a range between 0.45 and 1.1. As a result, the fuel particles impinging on the depression base are accelerated in such a way that the fuel particles are guided on to oxygen-rich zones in order to prevent an undesired concentration of fuel-rich zones in the depression base region.
According to a further embodiment of the invention, the compression projection is formed such that the highest compression projection region is spaced apart from the piston head by a minimum compression spacing, and a ratio of minimum compression spacing to maximum depression depth is in a range between 0.1 and 0.45, in particular between 0.15 and 0.25. A free space which is adapted to the depression depth is thereby provided between the injection nozzle and the compression projection, which free space serves to minimize the formation of fuel-rich zones in the region of the compression projection. The coordinated ratios proposed according to the invention provide favorable flow conditions which permit a required supply of air or oxygen to the fuel-rich zones in the region of the compression projection and of the piston depression base.
Further advantages can be gathered from the following description and the associated drawings. Exemplary embodiments of the invention are illustrated in the drawings.